The invention is drawn to genetic engineering of plants to improve agronomic performance, particularly for increasing water-use efficiency in plants.
Plant growth is often limited by the availability of water. In plants, the majority of all water loss occurs through pores on the leaf surface, which are called stomata. The sizes of the stomatal pores in a leaf are variable and control the rate of diffusion of water vapor out of the plant. In addition to controlling water loss, stomata allow CO2 to diffuse into the leaf for photosynthesis. This common pathway for gas exchange between the leaf and the atmosphere results in a large amount of water vapor escaping from the plant during the influx of CO2. However, stomatal aperture is typically substantially greater than that needed for maintaining maximal photosynthetic rates.
Each stomate is formed by two guard cells. Together, the two guard cells form a stomatal pore. Opening and closing of stomata are caused by specialized biochemical processes in the guard cells that occur in response to environmental changes. The pore is opened by an increase in osmotic pressure in the guard cells, which is the result of the uptake and synthesis of osmotically active compounds and a corresponding uptake of water. The increase in guard-cell volume causes the pore to open.
To minimize water loss from leaves, stomatal aperture is regulated. During water shortage, plants prevent dehydration by closing their stomata partially or completely. When water is not limiting and other environmental conditions favor photosynthesis and plant growth, stomata are open, allowing CO2 to enter for photosynthesis. Because plant growth is often limited by the availability of water and because the amount of water loss greatly exceeds CO2 uptake necessary for photosynthetic carbon reduction, molecular mechanisms are needed to increase water-use efficiency in plants.
An object of the present invention is to provide methods and compositions for improving water-use efficiency in plants.
Another object of the present invention is to provide methods and compositions for increasing drought tolerance in plants.
Another object of the present invention is to provide methods and compositions for increasing irrigation efficiency.
Another object of the present invention is to provide methods and compositions for increasing productivity under conditions when water is not limiting.
Another object of the present invention is to provide methods and compositions for increasing heat tolerance in plants.
The methods comprise engineering a plant to modify malate accumulation in the plant to alter stomatal conductance to water vapor. Polynucleotides capable of modifying the accumulation of malate in the plant can be used in cassettes or constructs for expression in plants or plant cells of interest. Transformed plants, tissues, and seeds having improved water-use efficiency are provided.
Methods for modulating stomatal aperture or altering water-use efficiency in a plant are provided, the methods comprise:
a) transforming a plant cell with a polynucleotide operably linked to a promoter that drives expression in a plant, wherein the polynucleotide is capable of modulating malate accumulation in the plant cell, with the proviso that when the polynucleotide encodes phosphoenolpyruvate carboxylase, the plant is other than potato or tobacco;
b) regenerating plants from the transformed cell; and
c) selecting for plants exhibiting an altered stomatal aperture or altered water-use efficiency or characteristic correlated to same.
Also provided are methods for increasing productivity in a plant comprising:
a) transforming a plant cell with a polynucleotide operably linked to a promoter that drives expression in a plant, wherein the polynucleotide is capable of modulating malate accumulation in the plant cell, with the proviso that when the polynucleotide encodes phosphoenolpyruvate carboxylase, the plant is other than potato or tobacco;
b) regenerating plants from the transformed cell; and
c) selecting for regenerated plants exhibiting improved productivity.